I think in this case it is more than just “lack of knowledge”, at least concerning the basic investment idea. Less than 1% beating the market can’t just be about knowledge, but in my opinion suggest something more fundamental preventing success. Otherwise there’d be more people finding success just acting randomly or consistently choosing the opposite of the consensus.

Imo at least concerning retail investors it is a disadvantage in speed and access to tools. And additionally fees from middlemen eating away potential profits at this smaller scale.

We don’t really now what exactly they are doing, but I imagine that something like Renaissance technologies’ medallion fund are arbitraging away any profits (after fees) to be had. They’ll be faster with their way better infrastructure and will use financial instruments in such complex ways the average investor can’t even imagine or access. I guess knowing where to look for these opportunities is a knowledge advantage, but not on an individual trade level, but a systematic one.